The present invention relates to the employment of a solution of a polyacrylic resin in a mixture of organic solvents as a primer composition to treat aromatic organic thermoplastic substrates. More particularly, the present invention relates to a method for applying a silicone hardcoat composition onto a primed aromatic thermoplastic substrate and to acrylic primer compositions used in such method.
Prior to the present invention, composites of silicone hardcoat compositions on an aromatic thermoplastic substrate, such as a polycarbonate substrate were made by initially priming the surface of the thermoplastic substrate with a thermally dried or baked acrylic primer which is shown in U.S. Pat. Nos. 4,242,381 and 4,284,685 which are incorporated herein by reference. Generally, an organic solvent solution or emulsion of a thermosetting acrylic resin with an ultraviolet light absorbing agent is applied onto the surface of the aromatic thermoplastic substrate and baked for one hour at 120.degree. to 125.degree. C. Additional heat cured acrylic primer compositions are shown by U.S. Pat. No. 4,486,565 and 4,382,109 which also are incorporated herein by reference. In a typical process, a primer is applied onto the aromatic thermoplastic substrate, air dried for 15 minutes and then baked for 15-60 minutes at about 125.degree. C. The treated part is then allowed to cool to room temperature for about 15 minutes and then coated with the silicone hardcoat composition. The overall processing time can be 2 hours or more where the thermally baked primer usually requires 2 sets of application chambers and ovens for the dual coat process.
It would be desirable therefore to provide alternate procedures for applying abrasion resistant silicone hardcoat composition onto aromatic thermoplastic substrates which do not require an extensive bake or cure time for the primer, followed by a cooling period. Such procedures would substantially reduce the overall processing time for making silicone hardcoat-thermoplastic substrate composites.